Diagnosis (P. inornata): The new species is distinguished from other species of the Trimeresurus (sensu lato) complex, with the exception of other members of the genus Popeia and some members of the genus Cryptelytrops Cope, 1860, by a long calyculate hemipenis without papillae (as described in Malhotra and Thorpe, 2004b). Popeia inornata is distinguished from members of Cryptelytrops by full separation of the first supralabial and nasal scales. It is distinguished from other members of Popeia by the absence of a red or orange lateral stripe in adult males. Both sexes of P. inornata are separated from P. popeiorum sensu stricto by low ventral scale counts (no higher than 156, compared to no lower than 158), and from both P. popeiorum and the southern clade species by green eye coloration, with the exception of West Malaysian representatives of the southern clade, from which P. inornata can be distinguished by low ventral scale counts alone (149 – 156 vs. 157 – 172). With respect to the classification of Regenass and Kramer (1981), P. inornata is distinguished from the Borneo population (T. p. sabahi sensu Regenass and Kramer, 1981) by the absence of a red or orange lateral stripe in adult males and by green eye coloration in both sexes. It differs from snakes from the Barisan range of western Sumatra (T. p. barati sensu Regenass and Kramer, 1981) in having a longer and less compact head, a coloration of interstitial skin and dorsal scale bases that forms black bands with narrow light blue interspaces (vs. no dark bands on uniformly bluish gray to blue interstitial skin), and lower and upper margins of supralabials and infralabials, respectively, that are distinctly blue in life (vs. bluish white to lighter blue). Popeia inornata is further distinguished from west Sumatran specimens by the dorsal coloration of the tail which in life is a well-defined and solid brick red with light margins on red dorsal scales (vs. a light brown to golden hue which is less clearly demarcated laterally). While Regenass and Kramer (1981) distinguished T. p. barati on the basis of lower midbody dorsal scale counts (17 – 19 vs. 21 in the rest of their T. popeiorum group), an additional specimen examined by Sanders, Malhotra, and Thorpe (unpublished) from west Sumatra has 21 scale rows. Additional morphological characters that can be used in combination to diagnose the new species are listed in Table 1; diagnostic molecular characters are given above (3.2).Popeia inornata is not known to share its geographic range with any other green pitviper species. It is easily distinguished from juvenile and adult male Tropidolaemus wagleri (Boie, 1827) by the distinct red and white pre- and postocular stripe, red and white dorsal bands or spots, and keeled scales on the lower side of the head possessed by the latter species. Adult females of T. wagleri are even more distinct from P. inornata due to their highly divergent, largely black and yellow coloration and relatively massive girth. The new species can be distinguished from Parias hageni (Lidth de Jeude, 1886) by the dorsal coloration and pattern of the tail, which in Pa. hageni is green with a few irregular reddish-brown spots, and solid reddish-brown only in about the distal half of the tail (vs. laterally well-defined and solid brick red from about the anal region to the tip in P. inornata).

Etymology

Etymology (P. inornata): The specific epithet inornata is an adjective in the feminine singular gender. The scientific name of the new species alludes to the fact that adult males of P. inornata lack ornamentation by a distinctive orange to brick red ventrolateral stripe, which is typically present in adult males of sexually dimorphic members of the genus Popeia, and that both sexes show reduction of the white lateral stripe.